Rotary blower with noise abatement jacket enclosure

ABSTRACT

A rotary blower with noise abatement jacket enclosure having multiple interconnected and synchronized parallel multi-lobe rotors with the same number of lobes for propelling flow from a suction port to a discharge port of an inner casing without internal compression. The noise abatement jacket enclosure is shaped to surround the blower and to conform generally to its body contours, but is oversized to provide adequate cooling spaces with outer skin of the blower. It comprises a forced air cooling jacket comprising an inner and outer cover, a sound absorbent layer comprising an inner and outer surface, the inner surface in contact with the blower outer cooling cover, and a sound barrier layer comprising an inner surface in contact with the outer surface of the sound absorbent layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of mechanicalvacuum pumps and blowers used in industrial and municipal applications,and more particularly relates to double rotor multi-lobe type blowerscommonly known as positive displacement rotary blowers or simply Rootsblowers, and more specifically relates to a Noise Abatement jacketenclosure for reducing noise transmission from rotary blowers.

2. Description of the Prior Art

Rotary blowers are widely used in industrial and municipal applicationssuch as for loading a bulk truck by pneumatic conveying bulk materialsor for cleaning municipal sewer lines by vacuum suction. They aredesired because of its unique performance characteristics inherent fromits rotary positive displacement nature: it delivers an almost constantflow at varying vacuum levels. The ability of varying pressure or vacuumat constant flow makes rotary blowers the ideal tools for pneumaticconveying applications where material clogging can be quickly clearedwith the increase of the discharge pressure or suction vacuum whilemaintaining the transfer capability.

Rotary blowers for use in municipal sewer cleaning applications,especially when used in residential areas, are required to meetstringent noise level requirements, such as those prescribed by OSHA.Rotary blowers tend to be very noisy, sometimes as high as 90-105 dBA ifuntreated, because of the sharp discharge flow pulsations and engagementof timing gears at high speed. The later is generally of high frequencyand radiates from blower body. From a system point of view, the primarysource of noise generation in a blower package is the rotary blower. Inaddition to the Rotary blower, there is an array of secondary sources ofnoise, such as the motor, the valves, and the silencer body. But theyare all about 10-20 dBA less than the noise level of the blower.

Noise generated by the aforementioned sources is propagated either byair or by structure. By introducing upstream and downstream silencers,been widely used in the industry, air borne noise transmitted throughair stream is greatly reduced. Effort are also made to reduce the noiselevel by lowering the pulsation inside the blower, such as the methoddisclosed in U.S. Pat. No. 4,215,977 to Weatherston by self-cancelling aportion of the pulsation with de-phasing. The commercial application ofthis technology is, for example, Roots WhispAir as explained inpublication “Roots Whispair Blowers”. However, its effectiveness islimited, only achieving 5-10 dBA reduction. Moreover, to reduce thestructure borne noise and the air borne noise radiated from blowersurface itself, one way is to increase the mass and stiffness of theblower. Such modification of the structure of the blower is expensiveand can affect manufacturability of the blower. Another way is toenclose the blower system in a room-like sound enclosure usuallyconsisting of 6 sided wall panels with sound absorbent material and hardreflection surfaces. Sound enclosure built in this fashion is generallyvery effective, reducing the noise levels up to 25 dBA, but it isexpensive, heavy and bulky, especially not practical for mobileapplications.

What is therefore needed is a device capable of achieving a high dampingand reduction of noise emitted from blower surfaces while being keptlight in mass, small in size and suitable for mobile application. Itwould further be preferable if the device could also serve to enhancethe heat transfer from the blower outer surfaces, so that they couldoperate more quietly, reliably and be used for mobile applications.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a noiseabatement jacket enclosure, with a shape generally conforming to blowerouter contours, for reducing noise transmission from a rotary blowerwhile maintaining small size, light weight and suitable for mobileapplication.

It is a further object of the present invention to provide a noiseabatement jacket enclosure for a rotary blower which comprises a forcedair cooling jacket with a shape generally conforming to blower outercontours to enhance the heat transfer from the blower outer surfaces, sothat they could operate more quietly, reliably and be used for mobileapplications.

It is a further object of the present invention to provide a noiseabatement jacket enclosure for a rotary blower which comprises a soundabsorbent layer comprising an inner and outer surface, the inner surfacein contact with the blower outer surface, and a sound barrier layercomprising an inner surface in contact with the outer surface of thesound absorbent layer.

It is a further object of the present invention to provide a noiseabatement jacket enclosure for a rotary blower which comprises a forcedair cooling jacket comprising an inner and outer cover, a soundabsorbent layer comprising an inner and outer surface, the inner surfacein contact with the blower outer cooling surface, and a sound barrierlayer comprising an inner surface in contact with the outer surface ofthe sound absorbent layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section front view of a preferred embodiment of thenoise abatement Jacket enclosure of the present invention with a forcedair cooling layer;

FIG. 2 is a cross-section side view of a preferred embodiment of thenoise abatement Jacket enclosure of the present invention with a forcedair cooling layer;

FIG. 3 is a cross-section top view of a preferred embodiment of thenoise abatement Jacket enclosure of the present invention with a forcedair cooling layer;

FIG. 4 is a cross-section front view of an alternative embodiment of thenoise abatement Jacket enclosure of the present invention with a forcedair cooling layer;

FIG. 5 is a cross-section side view of an alternative embodiment of thenoise abatement jacket enclosure of the present invention with a forcedair cooling layer;

FIG. 6 is a cross-section top view of an alternative embodiment of thenoise abatement jacket enclosure of the present invention with a forcedair cooling layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Although specific embodiments of the present invention will now bedescribed with reference to the drawings, it should be understood thatsuch embodiments are by way of example only and merely illustrative ofbut a small number of the many possible specific embodiments which canrepresent applications of the principles of the present invention.Various changes and modifications obvious to one skilled in the art towhich the present invention pertains are deemed to be within the spirit,scope and contemplation of the present invention as further defined inthe appended claims.

As a brief introduction, the present invention rotary blower with anoise abatement jacket enclosure includes an inner enclosed casinghaving a flow suction port and a flow discharge port and an internalbearing support structure, and an outer multi-layered cover, the noiseabatement jacket enclosure, comprising a forced air cooling jacketlayer, a sound absorbent layer, the inner surface in contact with theblower outer cooling layer, and a sound barrier layer comprising aninner surface in contact with the outer surface of the sound absorbentlayer. The noise abatement jacket enclosure is shaped to surround theblower and to conform generally to its body contours, but is oversizedto provide adequate cooling spaces between outer skin and the blower.

The present invention rotary blower with noise abatement jacketenclosure also includes two parallel multi-lobe rotors mounted on twoparallel rotor shafts respectively, where the rotor shafts are supportedby the internal bearing support structure of the inner casing andinterconnected through a set of timing gears to rotate the rotors insynchronization for propelling flow from the suction port to thedischarge port. Cooling fans are mounted on one of the two rotor shaftsat locations adjacent to the inlet and outlet openings of the outercover for circulating cooling air through the space between the outercover and the inner casing.

It is therefore an object of the present invention to teach theconstruction of a noise abatement jacket enclosure for reducing theradiation noise from blower outer surfaces. More specifically, the noiseabatement jacket enclosure of the present invention is a multi-layeredapparatus constructed to engage in contact with a rotary blower so as toboth reduce noise propagation and to act as a cooling path on the blowerouter surfaces. The present invention rotary blower with noise abatementjacket enclosure is capable of achieving lower noise level whilemaintaining being effectively cooled, light weight and compact size,thereby improving the blower application range for mobile andresidential areas.

Referring to FIGS. 1 to 3, there is shown a typical arrangement of apreferred embodiment of the rotary blower 10 with noise abatement jacketenclosure 50. Typically, the rotary blower 10 has two parallel rotors 12mounted on rotor shafts 14 and 16 respectively, where rotor shaft 14 isdriven by an external rotational driving mechanism (not shown) andthrough a set of timing gears 18 rotate the rotors 12 in synchronizationwithout touching each other for propelling the flow from a suction port36 to a discharge port 38 of the blower 10. The rotary blower 10 alsohas an enclosed casing 20, wherein the rotor shafts 14 and 16 aremounted on an internal bearing support structure 22 with bearings 24 andseals 26. The casing structure further includes an outer cover 28 with aspace maintained between the inner casing 20 and the outer cover 28 ascooling air passage 52 as indicated by the arrows for cooling flowdirection in FIG. 1 to 3. In FIG. 2, the large arrows show the directionof the internal flow as propelled by the rotors 12 from a suction port36 to a discharge port 38 of the blower 10.

As an important novel and unique feature of the present invention, anoise abatement jacket enclosure, is conformingly surrounding the rotaryblower 10 of the present invention, and its cross-section is illustratedin FIG. 1 to 3. In the embodiment illustrated, noise abatement jacketenclosure 50 is comprised of three layers. A first layer is comprised offorced air cooling path layer 52. A cooling fan 40 is employed on oneside of the blower to provide positive cooling air for the blower 10.The cooling fan is mounted on the extended shaft 14, adjacent to the airinlet openings 42 of the outer cover 28 for bringing in cooling air,which is in turn guided by the outer cover 28 to pass around the innercasing 20 through the space between the outer cover 28 and the innercasing 20 and exits from the air outlet openings 44 of the outer cover28, as shown by the arrows in FIGS. 1 and 3. The second and third layer,a preferably prefabricated combination of sound absorbent layer and asound barrier layer, is located in contact with the outer surface offorced air cooling jacket layer 52. The sound barrier layer 56 is usedto reduce sound transmitted to the ambient. The sound absorbent layer 54is preferably glued onto the sound barrier layer 56. In one embodiment,forced air cooling path layer 52 is in contact with sound absorbentlayer 54 which is itself attached to sound barrier layer 56 such thatthe entire assembly comprising noise abatement jacket enclosure 50 maybe fastened to rotary blower 10 and conforming to its outer contours.

When a rotary blower 10 is surrounded by the noise abatement jacketenclosure 50 of the present invention comprised of the forced aircooling layer 52 in contact with the sound absorbent layer 54 which isin contact with the sound barrier layer 56, there exists both areduction in the noise transmitted from the rotary blower to ambient aswell as an improvement in the cooling provided to the rotary blower.

The theory of operation underlying the noise abatement jacket enclosure50 of the present invention is as follows. The vibrating inner surfaces20 of the rotary blower 10 first is reflected by the cover 28, which isalso used to guide the cooling air around the blower outer contours.Then the vibrating surfaces 28 of the rotary blower 10 sets the soundabsorbent layer 54 in vibration and the vibration induced mechanicalenergy is turned into heat. It is of note that sound absorbent layer 54exhibit low stiffness, and as such, act as a decoupler between the soundbarrier layer 56 and the rotary blower casing 28. It is the purpose ofthe sound barrier layer 56 to again reflect sound waves back and forthbetween the sound barrier layer 56 and the rotary blower 28 therebyincreasing the dissipation of sound energy.

In the event that the rotary blower 10 outer surface 20 temperature isnot very high (typically lower than 120° F.), there is no need to havethe forced air cooling layer 52 to carry the heat away. In that case,the forced air cooling layer 52 is not needed and the rotary blower 10outer surface 20 is immediately followed by a sound absorbent layerlayer 54 which is itself surrounded by a sound barrier layer 56. In suchan instance, the combination of the sound absorbent layer 54 and thesound barrier layer 56 is sufficient to achieve the goal of the presentinvention.

FIGS. 4 to 6 show a typical arrangement of another preferred embodimentof the rotary blower 10 with noise abatement jacket enclosure 50. Inthis embodiment, the forced air cooling layer 52 is comprised of aninlet filter 62, a cooling fan 40, a cooling flow passage formed betweenthe outer cover 28 and the inner casing 20, manifold 64 and injectionports 66 and 68. The cooling air from fan 40, is guided by flow passage52 to the manifold 64, gathering for injection onto rotors 12 throughopenings 66 and into discharge port 38 through induction openings 68,exiting at discharge port 38, as shown by the arrows in FIGS. 4 to 6.

It is apparent that there has been provided in accordance with thepresent invention a noise abatement jacket enclosure for reducing noisetransmission in rotary blower. While the present invention has beendescribed in the context of specific embodiments thereof, otheralternatives, modifications, and variations will become apparent tothose skilled in the art having read the foregoing description.Accordingly, it is intended to embrace those alternatives,modifications, and variations as fall within the broad scope of theappended claims.

1. A rotary blower with noise abatement jacket enclosure, comprising: a.a housing structure having a flow suction port and a flow discharge portand internal flow passage there-between, and an inner enclosed casingand an outer cover with a hollow space there-between; b. two parallelmulti-lobe rotors having the same number of lobes and rotatably mountedon two parallel rotor shafts respectively inside said inner casing andinterconnected through a set of timing gears to rotate insynchronization for propelling flow from said suction port to saiddischarge port; c. a cooling layer comprising said space between outercover and said inner casing and at least one cooling fan mounted on oneof said two rotor shafts for circulating cooling air through said layer;d. a sound absorbent layer comprising an inner and outer surface, saidinner surface in contact with said outer surface of said cooling layer;e. and a sound barrier layer comprising an inner surface in contact withsaid outer surface of said sound absorbent layer; f. whereby said highrotary blower is capable of achieving a high damping and reduction ofnoise emitted from said blower surfaces while being kept light in massand small in size, and at the same time enhancing the heat transfer fromsaid blower outer surfaces, so that said blower operates more quietly,reliably and be used for mobile applications.
 2. The noise abatementjacket enclosure of claim 1, wherein said cooling layer has acentrifugal cooling fan mounted on one of said two rotor shafts forcirculating cooling air through said layer.
 3. The noise abatementjacket enclosure of claim 1, wherein said sound absorbent layer iscomprised of a material selected from the group consisting of expandableUrethane foam.
 4. The noise abatement jacket enclosure of claim 1,wherein said sound barrier layer is comprised of hard materials such asmetal or plastic.
 5. A rotary blower with noise abatement jacketenclosure, comprising: a. a housing structure having a flow suction portand a flow discharge port and internal flow passage there-between; b.two parallel multi-lobe rotors having the same number of lobes androtatably mounted on two parallel rotor shafts respectively inside saidinner casing and interconnected through a set of timing gears to rotatein synchronization for propelling flow from said suction port to saiddischarge port; c. a sound absorbent layer comprising an inner and outersurface, said inner surface in contact with said outer surface of saidblower housing; d. and a sound barrier layer comprising an inner surfacein contact with said outer surface of said sound absorbent layer; e.whereby said high rotary blower is capable of achieving a high dampingand reduction of noise emitted from said blower surfaces while beingkept light in mass and small in size, and at the same time enhancing theheat transfer from said blower outer surfaces, so that said bloweroperates more quietly, reliably and be used for mobile applications. 6.The noise abatement jacket enclosure of claim 5, wherein said soundabsorbent layer is comprised of a material selected from the groupconsisting of expandable Urethane foam.
 7. The noise abatement jacketenclosure of claim 5, wherein said sound barrier layer is comprised ofhard materials such as metal or plastic.
 8. A rotary blower with noiseabatement jacket enclosure, comprising: a. a housing structure having aflow suction port and a flow discharge port and internal flow passagethere-between, and an inner enclosed casing and an outer cover with ahollow space there-between leading to a manifold with injection portstowards rotor near discharge port; b. two parallel multi-lobe rotorshaving the same number of lobes and rotatably mounted on two parallelrotor shafts respectively inside said inner casing and interconnectedthrough a set of timing gears to rotate in synchronization forpropelling flow from said suction port to said discharge port; c. acooling layer comprising said hollow space between said outer cover andsaid inner casing and at least one cooling fan on each side mounted onone of said two rotor shafts for circulating cooling air through saidlayer; d. a sound absorbent layer comprising an inner and outer surface,said inner surface in contact with said outer surface of said coolinglayer; e. and a sound barrier layer comprising an inner surface incontact with said outer surface of said sound absorbent layer; f.whereby said high rotary blower is capable of achieving a high dampingand reduction of noise emitted from said blower surfaces while beingkept light in mass and small in size, and at the same time enhancing theheat transfer from said blower outer surfaces, so that said bloweroperates more quietly, reliably and be used for mobile applications. 9.The noise abatement jacket enclosure of claim 9, wherein said coolinglayer has a centrifugal cooling fan mounted at each side on one of saidtwo rotor shafts for circulating cooling air through said layer.
 10. Thenoise abatement jacket enclosure of claim 9, wherein said soundabsorbent layer is comprised of a material selected from the groupconsisting of expandable Urethane foam.
 11. The noise abatement jacketenclosure of claim 9, wherein said sound barrier layer is comprised ofhard materials such as metal or plastic.